Rough idle, engine code 1151..ideas?

[Blind]

Rough idle, engine code 0300..ideas?

Randomly the idle on my truck is perfectly smooth, then at random stops it's really rough, and the voltmeter needle dances around too.

I just:
changed fuel filter
changed plugs (autolite platinums, gap set to .052)
cleaned MAF sensor wires with electrical cleaner

I then hooked up my code reader and cleared the code, previously the code my check engine light gave me (I forget the #) was for a "random/multiple cylinder misfire" and I could see why, my plugs that came out were all around .082 gap.

The code it spit out tonight was for the secondary o2 sensor? How would the o2 have an effect on idle? My thoughts are it threw this code because of the unburnt fuel from the bad spark plugs and the o2 was just reading garbage air from the misfiring.

I test drove it a few minutes ago and it did the rough idle crap at a stoplight again, then the next stoplight I came to it idled perfectly smooth


any thoughts?

It's the exploder in my sig, 1996 4.0 OHV automatic 2wd, just turned 98k miles.

 

[Runnin'OnEmpty]

Mr Blind, code P1151 is "Lack of upstream HO2S switch, sensor indicates lean (bank #2)". This is the sensor located on the header pipe on the driver's side.
Since it's not switching, I'd first look for burnt wiring where the harness routes above the exhaust manifold. If that's OK, and the sensors are old, then I'd simply replace the sensor first. This code is from either a bad sensor or an intake manifold leak on the driver's side.

I don't think the P1151 is related to the poor idle, though. For that I'd clean the IAC, and see if that helps. It sounds like the IAC pintle rod is sticking occasionally. Give it a shot of WD-40 where it goes into the motor mechanism.

Good luck,
ROE

 

[Blind]

removed and cleaned the IAC, still running rough...at completely random times.

I'm thinking it's the coil packs or plug wires now.


I had the good fortune of having it do it when I parked at home tonight, and it did it in drive, then I put it in park and set the brake and it was still rocking and bucking and idling really ****ty, so I reved it up a bit and it was rough and hesitating all the way up to 2500, over 3k it seems fine but the missfire is probably happening too often for me to be able to feel it.

I'm not looking forward to pulling off the plug wires again, hopefully the come off easier from the new plugs than the old ones :roll:

 

[Runnin'OnEmpty]

Installing new plug wires would indeed be the next step. Since you got a random misfire code before changing the plugs, there could be a wire that's "tracking" and grounding out to give the erratic idle.

What did you do for the O2 code? Change the sensor?

 

[Blind]

What did you do for the O2 code? Change the sensor?

I'm going to ignore that until this random rough idle is fixed. I'm thinking the misfiring is casuing the o2 sensor on that side to read out of range, which is throwing that code, the code is thrown for the O2 sensor because it's reading is so far out of range the computer thinks it is missing, I'm pretty sure that's because unburned fuel is being thrown at it from the misfire.

 

[Blind]

changed the wires today, and cleared the code, the rough idle came back!

1151 code was not there this time. Today the code was 0300, which is the random / multiple cylinder misfire code.


next part to throw at it...coil pack???

 

[410Fortune]

have you cleaned the MAS???

Nobody mentioned cleaning the MAS. Also be very careful when gapping platinum tipped plugs, you can knock the platinum right off the end with the gapper....

Rought idle can sometimes be crappy gas (low octane), worn engine mounts and also the nature of the OHV V6 (they idle smooth but sometimes will ahve a slight stumble at a low idle.

You may try adjusting your idle stop screw just a hair to raise it a bit, only if its happening when the engine drops down to 600-800 rpm at a warm idle.

other things to consider:
fuel filter
vacuum manifold leak
your code

Okay so now you have another misfire code, I would check all the wires and make sure they are clean and fully seated in the coil pack and on each plug end.
A new code = start where you were last working (plugs/wires)

quit throwing parts at it! The coil packs VERY rarely need replacing....I have never seen one go bad or replaced one if that means anything.

 

[aldive]

quit throwing parts at it! The coil packs VERY rarely need replacing....I have never seen one go bad or replaced one if that means anything.

I concur.

 

[Blind]

what I have done:

removed and cleaned MAF sensor
removed and cleaned IAC valve
new motorcraft fuel filter
new motorcraft plug wires
new autolite platinum plugs gapped at 0.054

the plug wires are on correctly, they were installed with a squirt of dialectric grease on each end.

vacuum checks out at idle.

this is NOT a consistant thing, it will idle smooth as butter, then I drive it, and the next stop sign I get to it is bucking, and it will surge and buck on light throttle, if I give it WOT it will hesitate and then rev and accelerate normally.

 

[410Fortune]

test fuel pressure?
Does it get worse as it gets hot?
Still have a code?

 

[Blind]

fuel pressure is fine, I tested in 3 weeks ago so I forget what it was exactly but it matched what the tag on the radiator support called for.

cold/hot doesn't seem to matter.

when I installed the plug wires yesterday I reset the code, it was 0300 random/multiple cylinder misfire.